I would go with swiss ball training to train the lower body parts. One exercise you could do is lie down outstretched on the ground with your feet on the swiss ball. You start raising your body by pulling the ball towards you with your feet. Draw in the abs to stablize your back. This works your hips and glutes. It's called "Two feet stability ball hip extension". The instability works your legs better than weight training with machines. Once it gets easier, you could progress to one feet. Reference: Functional Training for Sports by Michael Boyle
If you read Boyle's more recent writings you'll see that he's moved away from doing a lot of those exercises.
And what was his reason for that? The swiss ball training exercise is working pretty well for me. The instability activates all the stabilizers and made my legs stronger.
Well, first of all, many people can't perform those exercises properly on stable ground, never mind with the added challenge of an unstable surface. By this I mean getting the correct muscles to fire in the correct sequence and the correct proportions. Secondly, unless your sport is log rolling or surfing or something like that, instability in sport doesn't come from the ground shifting away from under you. Instead it happens because you can't deal with excess momentum quickly enough.
Can our muscles really tell the difference between the ground giving way and deceleration? In both scenarios, stabilizers are needed to maintain balance. Granted these exercises are a challenge to perform properly for most people but they would benefit when given proper directions.
It's not about the muscles, it's about the motor programs. If the unbalancing forces are external, the body has to sense those external forces, process that information and tell the body to make adjustments to keep balance. When there is no externally applied force, then the lack of balance is because the body can't maintain the correct posture to stay balanced. I've seen a lot of trainers out there who miss many of the fine points of performing these exercises, while taking their clients to more and more ridiculously designed exercises involving unstable surfaces.
